The present invention relates to devices and methods for burning pyrotechnic compositions and more particularly to firework devices that rely on propulsion to produce colored flame displays.
The type of pyrotechnic devices for entertainment purposes are numerous, but most generally consist of flammable compositions that burn to produce colored flames or provide propulsion for colored flames and/or sparks. Some examples are lances, which produce a colored flame only and are typically used in large sets or arrays to produce figures (e.g. flags) or letters or words. Other devices known to the pyrotechnics industry hare xe2x80x9cflares,xe2x80x9d which produce an effect comparable to lances, but are generally larger in size. The devices called xe2x80x9cwaterfallsxe2x80x9d burn with or without colored flames and generate a large cascade of burning metal sparks. Color-producing pellets, referred to as xe2x80x9cstars,xe2x80x9d are employed in xe2x80x9cshellsxe2x80x9d or xe2x80x9croman candlesxe2x80x9d or xe2x80x9cstar minesxe2x80x9d and often contain stars in multiple amounts. Typically black powder is used to ignite and propel the stars out of such devices.
The devices called xe2x80x9cgerbsxe2x80x9d (also known as fountains) utilize pyrotechnic compositions to vertically propel burning metal sparks and in addition produce a colored flame. Among typical compositions for gerbs or fountains have been: (1) potassium nitrate, charcoal, sulfur, steel powder; or (2) potassium nitrate, strontium nitrate, potassium benzoate and titanium metal powder. Typical formulations for gerbs generally include a fast-burning fuel/oxidizer mix that contains metallic filings or powder. The metal filings or powder burns to produce various colored sparks depending on the type of metal used.
Commercial pyrotechnic devices, as for example, gerb devices, have typically used an end-burning configuration with a clay nozzle. The clay nozzle is often used to increase the pressure within the gerb device, which in turn creates the necessary pressurized gas flow to drive the burning sparks upward. A gerb is often made by pressing a clay nozzle into a cardboard tube. Subsequently, a small amount of priming mixture (prime) is pressed behind the clay nozzle followed by the pyrotechnic composition.
We have learned, however, that the end-burning configuration does not optimally produce a pyrotechnic display. Among the disadvantages presented by the present technology are that the clay nozzle restricts the size of the flame envelope and impurities such as sodium and calcium present in the clay cause flame discoloration. Further, it is difficult and impractical to remove such impurities from clay compositions. One solution has been to use larger amounts of flame colorants to overcome the flame discoloration caused by the clay impurities which in turn produces larger amounts of smoke and ash that may have detrimental environmental effects. Yet another disadvantage of the prior art is the frequency of misfiring due to the sensitivity of proper placement of an ignition source (typically done by the user) in an end-burning configuration.
As a result, a device with cleaner burning characteristics would require the use of less metallic flame colorant and consequently result in a lower smoke-producing pyrotechnic device. In addition, the efficacy of using low smoke producing pyrotechnic compositions as disclosed in related U.S. patent application Ser. No. 09/833,874 entitled xe2x80x9cLow-Smoke Nitroguanidine and Nitrocellulose Based Pyrotechnic Compositionsxe2x80x9d, which is incorporated herein by reference, would be enhanced, as lesser amounts of flame colorants are used in such low smoke producing compositions.
It is therefore an object of the invention to provide a pyrotechnic device and method that overcomes the problems presented in the prior art and allows a cleaner burning pyrotechnic device which thereby needs a lesser amount of colorants to achieve a desired pyrotechnic display. It is a further object of the invention to provide a pyrotechnic device and method whereby a faster burning device with a larger surface area of burning pyrotechnic composition may provide a more effective pyrotechnic display by increasing the propellant force characteristics of the pyrotechnic device.
It is yet another object of the invention to provide a pyrotechnic device and method that provides more reliable ignition characteristics.
It is yet another object of the invention to provide a pyrotechnic device and method whereby the rate of burn may be varied such that a variable burn rate may be advantageously used to alter visual effects in pyrotechnic displays.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a pyrotechnic composition including fuel (combustible material), an oxidizing agent, and at least one of a metal salt and metal powder, wherein the pyrotechnic composition comprises a cylinder with an internal surface area positioned within an outer cylindrical surface area; and, wherein prime is proximately disposed at least at one end of the internal surface area of said cylinder.
In another embodiment, the internal surface area and outer cylindrical surface area comprise a hollow cylinder.
In a related embodiment, the internal surface area comprises the adjacent surfaces internal to an outer cylindrical surface area formed by positioning a solid cylinder within a hollow cylinder.
In yet another embodiment, the internal surface area comprises a surface of a star-shaped opening within the cylinder extending axially to said cylinder.
In yet another embodiment, the internal surface area comprises an opening within the cylinder offset from the central axis of said cylinder extending axially through said cylinder.
In another embodiment, prime is disposed within the internal surface area said prime adjacent to an ignition source.
In another embodiment, the present invention further provides a cylindrical plug disposed adjacent to the at least one end of the hollow cylinder and including an opening in the cylindrical plug thereby allowing access to the prime.
In yet another embodiment, the present invention further provides an ignition source disposed through the opening in the cylindrical plug said ignition source adjacent to the prime.
Related embodiments of the present invention include a method of producing a pyrotechnic device according to the invention.